1. Field of the Invention
The present invention relates to wireless asset tracking with respect to bounded regions. More particularly, the present invention relates to systems and methods for reducing false positive geofence boundary crossing alert signals.
2. Description of the Related Art
Techniques for wireless asset tracking are known in the art. Global Positioning Satellite (“GPS”) based tracking systems have been employed for a number of years. Tracking movements of long haul truck assets is a known example of GPS based tracking systems. In such a system, an antenna and GPS receiver are mounted to a truck, and are further coupled to a wireless transceiver having access to a wireless network. The GPS receiver outputs position fixes, comprising latitude and longitude coordinates and other data, which are coupled to the wireless transceiver so that position reports can be communicated through the network and back to a central station. In this manner, the truck can be tracked as it moves about the roadways. In a monitored mode of operation, an operator at the central station located on the network observes the movement of the truck, looking for any excursions or inordinate time variances beyond what is expected for the particular truck. Such prior art systems have certain limitations. For example, since it is common knowledge that long haul trucks have GPS tracking systems, it is appreciated that disabling such a system will prevent the truck from being tracked.
The utilization of position reports communicated by tracked assets is an area of technology that has also advanced. In the preceding example, it can be appreciated that employing a person to continually monitor the movement of plural assets has a number of cost and reliability issues. Also, since most trucks operate along predetermined routes, it can be appreciated that giving careful attention to an asset that is located along its predetermined route is not an efficient use of a monitoring asset. Rather, it is excursions from the predetermined route that are of most interest. Thus, the concept of defining boundaries for areas of operation is known. The industry has defined a term to describe the boundaries of a predetermined area of operation, and that term is a “geofence”. More particularly, a geofence is a virtual perimeter for a real-world geographic area. Since many prior art tracking systems operate using latitude and longitude (“lat/lon”) coordinates, geofence boundaries have been defined in similar terms. For example, a radial geofence may be defined by its lat/long center position and a predetermined radius. Also, polygonal geofences may be defined using three or more lat/lon vertices with lines interconnecting them so as to define a bounded area. Thus, the extent of such a geofence definitions is mathematically determined and established with a precision of the lat/lon coordinates. In the case of GPS lat/lon fixes, the coordinates typically include degrees of lat/lon and minutes of angle to at least four decimal places. Thus, it can be appreciated that geofence boundary definitions and boundary excursion calculations are relatively precise and adaptable for computer based calculations and related processing.
Although GPS coordinate based tracking is known and somewhat prevalent in the prior art, it is not the only tracking technique known. Nor is GPS position determination necessarily preferred for certain applications. For GPS receivers to produce reliable and accurate position fixes, the antenna must have clear ‘view’ of three GPS satellites, and preferably four. With an unobstructed view from horizon to horizon a high degree of reliability can be achieved. However, in real-world tracking environments, the skies are not so unobstructed and weather is a significant factor as well. Also, not all assets are moving assets located out of doors. When an asset is locate adjacent to or within a building or structure, GPS reliability drops precipitously. Thus, other location determining technologies have been employed. The LORAN terrestrial based navigation system is known, which employs radio triangulation from plural fixed position radio transmitters. Similarly, there are a number of fixed radio transmitter location networks that can be utilized in asset tracking application. Cellular telephone transmitter sites are one example. Increasingly, other fixed radio transmitter networks are being deployed, including IEEE 802.11(WiFi) networks, IEEE 802.16 (WiMax), Bluetooth, and other LAN and WAN telecommunications networks. These networks can be employed for location determination for asset tracking purposes. And, geofence boundaries can be defined in terms compatible with the locating techniques employed.
The accuracy of geofence boundary definitions can be rather precise, as was discussed above. So too can the apparent accuracy of position fixes. Thus, it appears to be a simple computational task to extract a position fix from a position report communicated from a tracking device coupled to an asset, and then compare it to a predetermined geofence boundary definition to determine if a geofence boundary excursion has occurred. However, the real-world experience is that while position fixes have apparent precision, they commonly do not posses actual precision. For example, a GPS tracking device will report a fix with six to seven significant digits in the lat/lon coordinates, yet that fix may deviate several hundred meters from the physical geographic location of the asset. The vagaries GPS radio propagation and receiver errors are significant, and generally degrade with weather and obstructions. Thus, the reported position of a fixed position asset may come to appear random when comparing multiple reports over time. The net result is that when an asset is located physically close to a geofence boundary, the probability of false positive excursion reports increases.
Of course, degrees of accuracy are more or less significant depending on the application and metrics of the geofence containment requirements. The other tracking technologies, as will be more fully discussed herein, suffer from similar accuracy and false positive excursion reports. Since an essential function of an asset tracking system that relies on predetermined boundaries is to report excursion therefrom, the likelihood of false positive excursion reports is problematic. Generally speaking, when an asset is contained within a geofence boundary, the user or owner of the asset commits no action, and consumes no additional assets beyond normal operation. However, where there is a geofence excursion report, some reaction or corrective action is generally required. Thus, a false positive excursion report is tantamount to a false alarm, the reaction to which can be costly. Furthermore, repeated false positive excursion reports tend to degrade confidence in the tracking operation as a whole, and may lead to the situation where true positive reports are ignore. Thus, it can be appreciated that there is a need in the art from a systems and methods for reducing false positive geofence boundary crossing reports and alert signals.